This application will study molecular events of mammalian sperm-egg interaction to provide new information about the mechanism of fertilization. A mammalian sperm protein which is known to interact with the egg will be studied in mice. The long term objective is to understand the molecular basis of fertilization events, starting with the sperm membrane protein heterodimeric fertilin, whose a,b subunits are members of a protein family called, ADAM (A Disintegrin and A Metalloproteinase Domain) or MDC (Metalloproteinase/Disintegrin/ Cysteine-rich). Because the disintegrin domains in fertilin have homology to a family of ligands for integrin adhesion molecules and previous studies have provided evidence that fertilin is involved in sperm-egg interaction, this proposal will study the roles of these disintegrin domains of a and b fertilin in sperm-egg adhesion, in the mouse model. Aim 1 will characterize the roles of the disintegrin domains of fertilin a and b in fertilization by testing if selected amino acid sequences in these domains mediate binding of fertilin a and b to the egg, or inhibit the binding of sperm to eggs. Aim 2 will identify the binding partners of fertilin a and b by using recombinant forms of these sperm proteins as probes to identify binding partners on mouse eggs, on cultured cells, and in phage display libraries. Aim 3 will examine the possible involvement of fertilin a and b in egg activation by determining whether recombinant forms of fertilin a and/or b induce egg activation events, e.g., the rise in egg intracellular calcium or the polyspermy block. In terms of significance, the proposal states that, first, the results of these studies will be relevant clinically to contraceptive development and understanding forms of infertility; and, second, because fertilin a and b are the best characterized ADAM/MDC members, furthering our knowledge of fertilin will elucidate possible cell adhesion and signal transduction roles of other members in this family.